Function repository_get_stream_selection 

pub async fn repository_get_stream_selection(
    manager: State<'_, RepositoryManagerWrapper>,
    handle: String,
    item_id: String,
    media_source_id: Option<String>,
    audio_stream_index: Option<i32>,
) -> Result<StreamSelection, String>

Decide what stream to play for a video, and describe it.

Replaces repository_get_video_stream_url for playback. The returned StreamSelection carries the transport explicitly, so the frontend picks its loader from a tagged enum instead of testing the URL for .m3u8; and it carries the quality ladder as it applies to this source, so the picker can stop offering rungs that produce the same bytes as Original.

No start-position parameter, for the same reason as the URL builder: a position on an HLS playlist is copied onto every segment URI and the server rejects each with 400 (DR-181). Callers resume by seeking after load.

TRACES: UR-070, UR-079 | DR-225, DR-227, DR-228 | UT-213